Fiber-reinforced polymer composites are well known and widely used. Polymers of improved strength and increased stiffness can be obtained by the use of an appropriate reinforcing fiber. Probably the most widely used reinforcing fibers are glass, carbon and aramid (or "Kevlar" which is a registered trademark of the E. I. du Pont de Nemours & Co., Wilmington, Del.)
The base polymers used in making reinforced polymer composites such as those described above include a wide range of thermoplastics, such as polyethylene, polystyrene and copolymers thereof, polyamides, polycarbonates, polyetherimide and polyesters such as polybutyl terephthalate. These polymers are thermoplastics and are either amorphous or semi-crystalline. They may be called flexible chain polymers, since individual monomer units in the polymer chain are free to rotate with respect to each other so that the polymer chain may assume a random shape.
More recently developed are self-reinforced polymer composites comprising long, continuous, predominantly unidirectionally oriented fibers of a melt processable wholly aromatic polyester in a matrix of a thermoplastic flexible chain polymer. Such polymer composites are described in the co-pending, commonly assigned, U.S. patent application of Avraam Isayev and Michael J. Modic, Ser. No. 901,573, filed Aug. 29, 1986, now U.S. Pat. No. 4,728,698, issued Mar. 1, 1988. As described therein, the fibers of the wholly aromatic polyester, which may also be termed a thermotropic liquid crystal polymer (LCP) are formed in situ by mixing the matrix of base polymer with the wholly aromatic polyester in a suitable mixing and extrusion apparatus, as for example an extruder-static mixer setup, or a twin screw extruder. Polymer composites specifically disclosed therein are polycarbonate/LCP composites containing from 2.5 to 50 weight percent of LCP, and polyetherimide/LCP composites containing from 5 to 30 percent by weight of LCP. Polycarbonate/LCP composites exhibited long continuous fiber structure only in compositions containing 2.5, 5 or 10 percent by weight of LCP; compositions containing either 25 or 50 percent of LCP did not exhibit long continuous LCP fibers and had inferior mechanical properties. On the other hand, polyetherimide/LCP composites had long continuous LCP fibers over the entire composition range tested (5 to 30 weight percent of LCP). The highest tensile strength realized in any of those blends was 151 mega pascals (MPa) (in a blend containing 10 percent by weight of LCP). Tensile modulus (in giga pascals, or GPa) appear to rise continuously with increasing LCP content, although the rate of increase appeared to level off or decay between 20 and 30 percent by weight of LCP. Maximum impact strength was achieved at 10 percent LCP loading, and composites containing either 20 or 30 percent by weight of LCP had lower impact strengths than did composites containing 10 percent LCP. In short, some of the physical properties of polyetherimide/LCP composites described therein were in general superior to those of pure polyetherimide, but nevertheless fell short of the properties required in some high performance applications.